1. Field
The present invention relates generally to communication, and more specifically to a buffer-based pilot searcher for wireless (e.g., GPS and CDMA) communication systems.
2. Background
Wireless terminals (e.g., cellular phones) are designed to provide various types of communication such as voice, data, and so on. These terminals may be capable of communicating with one or more wireless communication systems such as code division multiple access (CDMA), time division multiple access (TDMA) (e.g., GSM systems), and frequency division multiple access (FDMA) systems. Newer generation terminals may also be designed to support other services such as position determination, enhanced emergency 911 (E-911) service, and possibly others. For these services, the terminals may be capable of receiving transmissions from Global Position System (GPS) satellites.
A terminal typically needs to acquire signals transmitted from one or more transmitters (e.g., base stations, GPS satellites) in order to receive or exchange data with a given system. In many wireless communication systems, a pilot is transmitted from each transmitter to assist the terminals perform a number of functions. The pilot is typically generated based on a known data pattern (e.g., a sequence of all zeros) and using a known signal processing scheme (e.g., covered with a known channelization code and spread with either a known pseudo-random noise (PN) sequence or a known scrambling sequence). For some CDMA systems, each base station may be assigned a specific PN offset (e.g., for IS-95 and cdma2000 systems) or a specific scrambling sequence (e.g., for W-CDMA or UMTS system) that is different from those of neighboring base stations to allow the terminals to distinguish the individual base stations. The pilots from the transmitters may be used at the terminals for acquisition, frequency and timing synchronization, channel estimation, data demodulation, and so on.
A searcher is typically used to search for pilots in a received signal. The search for pilots is made challenging due to various physical phenomena and design constraints. First, the pilot is distorted by noise and interference in the communication link, which can make detection of the pilots difficult at the terminal. Second, the searcher may be required to search for pilots in different types of signals, such as CDMA and GPS signals. A searcher design that can provide the required functionality with reduced circuit complexity, size, cost, and power consumption is highly desirable.